docs: def forget_subject(sid):
      '''
      forget_subject(sid) causes neuropythy's freesurfer module to forget about cached data for the
        subject with subject id sid. The sid may be any sid that can be passed to the subject()
        function.
  
      This function is useful for batch-processing of subjects in a memory-limited environment; e.g.,
      if you run out of memory while processing FreeSurfer subjects it is possibly because neuropythy
      is caching all of their data instead of freeing it.
      '''
      sub = subject(sid)
      if sub.path in subject._cache:
          del subject._cache[sub.path]
      else:
          for (k,v) in six.iteritems(subject._cache):
              if v is sub:
                  del subject._cache[k]
                  break
      return None